How to add last Online to admin's Users list?

I installed the Simple Onlinelist plugin and got it to display the last online time on a user’s profile page, and the currently online users on the frontpage.

What I would really like is to have that item in the Admin’s list of users, as a new column. I looked at /bb-admin/users.php and can’t make heads or tails out of it, as it appears to draw its data from a variable or function or something that is elsewhere.

I’m just using kakumei, which doesn’t seem to have anything relevant in its folder.